It is well known that glaucoma is a potentially debilitating group of ophthalmic diseases associated with a high risk of blindness. These conditions include, but are not limited to: open-angle glaucoma, closed-angle glaucoma, neovascular glaucoma, normal pressure glaucoma, exfoliation and pigmentary glaucoma. Common to all of these glaucoma conditions is the inability of the eye to sufficiently balance the secretion of aqueous humor from the ciliary body with its removal via the trabecular meshwork (TM), thereby elevating intraocular pressure (IOP). The ocular hypertension associated with glaucoma causes a gradual degeneration of the retinal ganglion cells, whose axonal outputs make up the optic nerve. As retinal ganglion cells die, vision is slowly lost, generally starting from the periphery of the visual field. Often, the loss of vision is unnoticeable until significant nerve damage has occurred.
Loss of vision from glaucoma is irreversible. Recent prevalence figures from the National Institutes of Health and the World Health Organization regarding glaucoma indicate that glaucoma is the second leading cause of blindness in the U.S. and the first leading cause of preventable blindness. It is estimated that over 3 million Americans have glaucoma, but only half of them know they have it, most suffering from what is known as open angle glaucoma. Approximately 120,000 of those people are blind from glaucoma, accounting for 9%-12% of all cases of blindness. Glaucoma accounts for over 7 million visits to U.S. physicians each year. In terms of Social Security benefits, lost income tax revenues, and health care expenditures, the annual cost to the U.S. government alone is estimated to be over $1.5 billion. The worldwide number of suspected cases of glaucoma is around 65 million. Although glaucoma as such cannot be prevented, its consequences can be avoided if the disease is detected and treated early.
Today there are a variety of therapeutic options available for treating glaucoma. Invasive surgical intervention (trabeculectomy) is typically used as a last resort. Front-line therapy is the use of drugs to lower IOP. However, drugs don't work for many patients. The preponderance of these open angle glaucoma cases is presently addressed by laser therapies, such as Argon Laser Trabeculoplasty (ALT) and Selective Laser Trabeculoplasty (SLT). Both ALT and SLT procedures require placement of approximately 50 evenly spaced laser spots per 180 degrees of arc on a patient's trabecular meshwork (TM). Spot diameters of 50 μm and 400 μl are typical for ALT and SLT, respectively. ALT treatments usually involve only 180 degrees of a patient's trabecular meshwork (TM), while SLT is often delivered to the entire circumference for a total of 100 spots. Both of these therapies are tedious and time consuming for doctor and patient, as the laser treatment spots are applied manually and sequentially. Both ALT and SLT treat the TM with light that is predominantly absorbed by the melanin residing therein. The main difference between SLT and ALT, however, is the pulse duration of the therapeutic light. SLT uses short pulses (a few nanoseconds) to substantially spatially confine the heat produced to the targeted melanin particles, which is why SLT is considered to be “selective” or “sub-visible” therapy, while ALT uses longer pulses (100 ms) causing diffused thermal damage to the TM itself, and is known as standard, or “coagulative” therapy.
The diagram on an eye is shown in FIG. 1, and includes a cornea 1, an iris 2, an anterior chamber 3, a pupil 4, a lens 5, a ciliary body 6, trabecular meshwork TM 7, conjunctiva 8, sciera 9, and an angle 10. The fluid flow is shown by the arrows in FIG. 1. As can be seen from this figure, optical treatment of the TM would require light entering tire eye at a very shallow entry angle.
In U.S. Pat. No. 5,549,596, Latina discloses a method for the selective damaging of intraocular pigmented cells which involves the use of laser irradiation, while sparing nonpigmented cells and collagenous structures within the irradiated area. This method is useful for the treatment of glaucoma (SLT), intraocular melanoma, and macular edema. Latina discloses the basic method of selective therapy using pulsed lasers. However, sequential alignment and delivery of individual pulses is tedious and time consuming. In addition, since SLT treatment does not produce visible changes in the TM, accurate alignment of the next spot relative to the previously treated area is difficult.
In U.S. Pat. Nos. 6,059,772 and 6,514,241, Hsia, et al disclose a non-invasive apparatus and method for treating open angle glaucoma in a human eye by thermally ablating a targeted region of the TM using pulsed radiation having a wavelength between 350-1300 nm, energy of 10-500 mJ, and pulse duration of 0.1-50 μs. Here pulses slightly longer than those employed with SLT are used. However, Hsia et al. also do not address the tedious and time consuming effects of aligning and delivering individual pulses.
In U.S. Pat. No. 6,682,523, Shadduck discloses a system for non-invasive treatment of a patient's trabecular meshwork to treat glaucoma. The system and technique applies energy directly to media within clogged spaces in a patient's TM to increase aqueous outflow through the laser irradiation of microimplantable bodies (nanocrystalline particles) carrying an exogenous chromophore which are placed in the deeper regions of the TM. This causes thermoelasticaily induced microcavitation that serves to ablate the debris and accumulations therein. This approach is similar to that of Latina in that it requires the use of short pulses, and so should be considered as “selective” therapy. Unlike Latina, however, it makes use of an exogenous chromophore. The choice of wavelength for the treatment light source is no longer dependent upon melanin absorption, but instead will be primarily concerned with the absorption of this exogenous chromophore. However, Shadduck also fails to address the tedious and time consuming effects of aligning and delivering individual pulses.
FIG. 2 shows a typical gonioscopic lens assembly used to access the TM. Such lens assemblies are presently required to redirect light into the eye at very shallow entry angles so the light will reach the TM. This assembly includes a gonioscopic mirror 14 to reflect the light into the eye at shallow entry angles.
One proposed solution is the optical scanning system and method in U.S. Published Application 2005/0288745 A1, which is incorporated herein by reference. This published application discloses a scanning device used in conjunction with an ophthalmic contact lens assembly to project patterns of light onto the trabecular meshwork, as illustrated in FIG. 17 of that application (reproduced as FIG. 3 herein). In the embodiment shown, the gonioscopic mirror 62 within the contact lens 60 is made to rotate in conjunction with the output of the scanner 48 under the control of the controller 22 to allow for a complete 360 degree treatment of the trabecular meshwork. However, some physicians prefer to have more direct control over the rotation of the mirror (i.e. manual control in conjunction with visualization of the target tissue before each application of treatment patterns). In addition, it can be difficult to keep the alignment of the laser beam with the trabecular meshwork at all angular positions of the rotating gonioscopic mirror.
Accordingly, there is a need for a simple and flexible patterned (multi-location) treatment of the trabecular meshwork of a patient, where the physician has direct control over the rotation of the gonioscopic mirror, yet the system provides visual guidance to ensure patterns of treatment light can be pieced together without overlap or excessive gaps regardless of their visibility.